Residential homes and other buildings with basements often have one or more built-in crocks or sump pits, which are holes designed to collect water that has accumulated around the home's foundation. A sump pump is typically installed in the sump pit to remove any accumulated water. Such sump pumps combine an electric motor with a fluid pump and are usually powered through the home's 120 VAC electrical system. Since power outages can occur for many known reasons, including as a result of heavy storms, when sump pumps are needed the most, homes can also be equipped with a secondary, battery-operated, backup sump pump. The backup sump pump is typically powered by a conventional 12 VDC battery, such as a lead-acid marine or deep cycle battery. The backup battery is often connected to a trickle-charge battery charger in order to ensure the battery is charged when it is needed.
FIG. 1 illustrates a common installation of a primary sump pump 50 in a sump pit 52. When installing the primary sump pump 50, a check valve 54 is often installed downstream from a discharge 56 of the primary sump pump 50 to prevent flow of the water back into the sump pit 52. In the configuration of FIG. 1, a backup sump pump would be installed so that the discharge of the backup sump pump would connect into a pipe 58 between the discharge 56 and the upper surface of the sump pit 52. In such a configuration, if the backup sump pump were to turn on, the natural flow of water from the discharge 56 of the backup sump pump would be down through the primary sump pump 50 and back into the sump pit 52 (i.e., the path of least resistance). Therefore, in conventional backup sump pump installations, an installer must cut the pipe 58, pull the pipe 58 and the primary sump pump 50 out of the sump pit 52, and make sure there is a check valve at the discharge 56. If there is no check valve at the discharge 56 (e.g., because the check valve 54 was installed outside of the pit), the installer must obtain another check valve, remove the pipe 58 from the primary sump pump 50, install the new check valve at the discharge 56, re-cut the pipe 58 to a suitable length, and glue/attach the pipe 58 to the new check valve.
Both primary sump pumps and backup sump pumps typically include a common liquid level control switch consisting of a mercury switch embedded in a foam or plastic “float” housing. The fluctuating liquid level would cause the float to physically move, which would cause the mercury switch to close or open a circuit, depending on whether the mercury switch was normally open or normally closed. Mercury float switches were the industry standard due to their extreme reliability in harsh working environments. However, increasingly stringent regulations regarding products containing mercury have caused the industry to begin a shift toward alternative solutions for the mercury float switch. Currently, the most common alternative is the mechanical float switch.
Although there are several design variations of mechanical float switches on the market, the general perception is that they lack the reliability of the mercury switch design due to a multitude of moving parts inside the float housing. The moving parts can degrade operation by becoming misaligned, damaged due to impact in shipping and/or operation, corrode and cease to operate, become damaged due to electrical arcing and/or chattering, as well as many other failure modes.
The float is typically positioned in the liquid to be sensed. This can lead to problems with residue buildup and/or floating debris, causing the switch to degrade and eventually fail.